Conventionally, a relief valve is known which comes into an open state when the fluid pressure of a fluid flowing in from an inflow channel exceeds a given pressure, and thereby allows passage of the fluid (for example, see PTL 1). A relief valve disclosed in PTL 1 includes a valve hole, into which a valve element is inserted, and a valve chamber that accommodates the valve element. An urging force in a direction to bring the valve element into contact with the valve hole is also applied to the valve element from a spring.
The relief valve disclosed in PTL 1 comes into a closed state in which the valve element is in contact with the valve hole when a fluid pressure on an inflow channel side (a primary side) is lower than a given pressure. On the other hand, when the fluid pressure on the inflow channel side reaches the given pressure or more, the fluid pressure of the fluid in the vicinity of the valve hole acts to apply a force overcoming the urging force from the spring to the valve element. The valve element moves away from the valve hole to cause the fluid in the inflow channel to flow into the valve chamber through the valve hole. The fluid farther flows out to an outflow channel front the valve chamber.